Device with upper conductive element, lower conductive element, and insulating element

ABSTRACT

A liquid crystal display device comprising a pair of substrates with liquid crystal layer therebetween, a plurality of gate signal lines and a plurality of drain signal lines formed on one of the pair of substrates, at least a pixel electrode and a plurality of counter electrodes formed on the one of the pair of substrates in each pixels, at least one of the plurality of counter electrodes extend along a drain signal line overlapping to the drain signal lines with at least one of an insulation film therebetween, and the drain signal line has two or more regions which differ in distance between a surface of the drain signal line and the counter electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser.No. 10/270,664 filed on Oct. 16, 2002 now abandoned. Priority is claimedbased on U.S. application Ser. No. 10/270,664 filed on Oct. 16, 2002,which claims priority to Japanese Patent Application No. 2001-347190filed on Nov. 13, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly to a so-called in-plane type liquid crystal displaydevice.

2. Description of the Related Art

In a so-called in-plane type liquid crystal display device, a pair ofsubstrates are arranged to face each other while sandwiching liquidcrystal therebetween, a pixel electrode and a counter electrode whichare disposed close to each other are formed on each pixel regionprovided to a liquid-crystal-side surface of one substrate out of thepair of substrates, and the behavior of the liquid crystal is controlledin response to parallel components of an electric field to the substratewhich is generated between these electrodes.

As such a liquid crystal display device adopting an active matrix type,there has been known a liquid crystal display device in which, on theliquid-crystal side of one substrate, each pixel region is defined by aregion which is surrounded by a plurality of gate signal lines which arearranged in parallel and a plurality of drain signal lines which crossthe gate signal lines and are arranged in parallel. Further, in eachpixel region, a thin film transistor which is operated in response to ascanning signal from the gate signal line, a pixel electrode to which avideo signal is supplied from the drain signal line through the thinfilm transistor, and a counter electrode to which a voltage signalconstituting reference with respect to the video signal is supplied areformed.

Then, the pixel electrode and the counter electrode are respectivelyformed in a strip shape extending in one direction and they are formedof a group consisting of a plurality of electrodes in which the pixelelectrode and the counter electrode are arranged alternately.

Further, in such a constitution, there has been known the counterelectrodes which are formed such that the counter electrodes areoverlapped to the drain signal lines in the running direction of thedrain signal lines by way of an insulation film.

A line of electric force of the electric field from the drain signalline is configured to be terminated to the counter electrode which isformed to be overlapped to the drain signal line, while the line ofelectric force of the electric field is configured to be not terminatedto the pixel electrode which is arranged close to the counter electrode.This is because that when the line of electric force of the electricfield is terminated to pixel electrode, this generates noises.

SUMMARY OF INVENTION

However, with respect to the liquid crystal display device having such aconstitution, to make the counter electrode have the above-mentionedfunction, it is necessary to form the counter electrode such that awidth thereof is larger than a width of the drain signal line.

Accordingly, capacitance of the drain signal line with respect to thecounter electrode (parasitic capacitance) is increased and hence, it hasbeen pointed out that the delay of waveform is generated with respect tothe video signal supplied to the drain signal line.

In this case, the delay of waveform of the drain signal line isproportional to a product of resistance R of the drain signal line andthe parasitic capacitance C. Then, to improve the delay, it is effectivethat making at least one of the resistance R and the parasiticcapacitance C to be small.

However, in case that the counter electrode is present above the drainsignal line, even when the width of the drain signal line is increasedso as to reduce the resistance R of the drain signal line, the parasiticcapacitance C thereof with the counter electrode is increasedcorresponding to the reduction of the resistance R and, as a result,there arises a situation that the delay of waveform cannot be reduced.In other words, there are trade-off relation.

The present invention has been made in view of such circumstances andone advantage of the present invention lies in the reduction of acapacitance of a drain signal line with respect to a counter electrode.

To briefly explain the summary of typical inventions among theinventions disclosed in the present application, they are as follows.

(1)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality of drainsignal lines which cross the gate signal lines and are arranged inparallel are formed;

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes which generate electricfields between the pixel electrodes and the counter electrodes areformed on the pixel region; and

the counter electrodes include the counter electrodes which extend inthe running direction of the drain signal lines by way of an insulationfilm and are overlapped to the drain signal lines, and the drain signallines are constituted such that the drain signal line has regions whichdiffer in at least two or more stages with respect to a distance betweena surface of the drain signal line which faces the counter electrode andthe counter electrode.

(2)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality of drainsignal lines which cross the gate signal lines and are arranged inparallel are formed;

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes which generate electricfields between the pixel electrodes and the counter electrodes areformed on the pixel region; and

the counter electrodes include the counter electrodes which extend inthe running direction of the drain signal lines by way of an insulationfilm and are overlapped to the drain signal lines, and the drain signallines are constituted such that a taper which is flared toward a groundlayer side of the drain signal line is formed on at least a side wallface of one of respective sides in the running direction of each drainsignal line.

(3)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal there between, a plurality of gatesignal lines which are arranged in parallel and a plurality oftwo-layered conductive drain signal lines which cross the gate signallines and are arranged in parallel are formed;

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes which generate electricfields between the pixel electrodes and the counter electrodes areformed on the pixel region; and

the counter electrodes include the counter electrodes which extend inthe running direction of the drain signal lines by way of an insulationfilm and are overlapped to the drain signal lines, and the drain signallines are constituted such that a taper which is flared toward a groundlayer side of the drain signal line is formed on at least a side wallface of one of respective sides in the running direction of a conductivelayer which constitutes a lower layer side of the drain signal line.

(4)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality of drainsignal lines which cross the gate signal lines and are arranged inparallel are formed;

the drain signal line has a two-layered structure including a conductivelayer which constitutes a lower layer made of Al or an alloy thereof;

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes which generate electricfields between the pixel electrodes and the counter electrodes areformed on the pixel region; and

the counter electrodes include the counter electrodes which extend inthe running direction of the drain signal lines by way of an insulationfilm and are overlapped to the drain signal lines, and the drain signallines are constituted such that a taper which is flared toward a groundlayer side of the drain signal line is formed on at least a side wallface of one of respective sides in the running direction of theconductive layer which constitutes the lower layer of the drain signalline.

(5)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality oftwo-layered conductive drain signal lines which cross the gate signallines and are arranged in parallel are formed;

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes which generate electricfields between the pixel electrodes and the counter electrodes areformed on the pixel region; and

the counter electrodes include the counter electrodes which extend inthe running direction of the drain signal lines by way of an insulationfilm and are overlapped to the drain signal lines, and the drain signallines are constituted such that by etching a conductive layer whichconstitutes a lower layer of the drain signal line using a conductivefilm which constitutes an upper layer as a mask, tapers which are flaredtoward a ground layer side of the drain signal line are formed on sidewall faces of the conductive film which constitutes the lower layer ofthe drain signal line.

(6)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality of drainsignal lines which cross the respective gate signal lines and arearranged in parallel are formed;

the drain signal line has a three-layered structure in which anintermediate layer is formed of a conductive layer made of Al or analloy thereof and an uppermost layer and a lowermost layer are formed ofconductive layers made of material other than Al or an alloy thereof,

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes which generate electricfields between the pixel electrodes and the counter electrodes areformed on the pixel region; and

the counter electrodes include the counter electrodes which extend inthe running direction of the drain signal lines by way of an insulationfilm and are overlapped to the drain signal lines, and the drain signallines are constituted such that a width of the conductive layer whichconstitutes the lowermost layer is wider than a width of the conductivelayer which constitutes the uppermost layer, and a width of theconductive layer which constitutes the intermediate layer is changedfrom the width of the conductive layer which constitutes the lowermostlayer to the width of the conductive layer which constitutes theuppermost layer.

(7)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality of drainsignal lines which cross the gate signal lines and are arranged inparallel are formed;

the drain signal line has a three-layered structure in which anintermediate layer is formed of a conductive layer made of Al or analloy thereof and an uppermost layer and a lowermost layer are formed ofconductive layers made of material other than Al or an alloy thereof,

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes which generate electricfields between the pixel electrodes and the counter electrodes areformed on the pixel region; and

the counter electrodes include the counter electrodes which extend inthe running direction of the drain signal lines by way of an insulationfilm and are overlapped to the drain signal lines, and the drain signallines are constituted such that a width of the conductive layer whichconstitutes the lowermost layer is wider than a width of the conductivelayer which constitutes the uppermost layer, and a width between sidewall surfaces of the conductive layer which constitutes the intermediatelayer is changed from the width of the conductive layer whichconstitutes the lowermost layer to the width of the conductive layerwhich constitutes the uppermost layer, and oxide films are formed on theside wall surfaces.

(8)

A liquid crystal display device according to the present invention is,for example, characterized in that:

on a liquid-crystal-side surface of one substrate of respectivesubstrates which are arranged to face each other in an opposed mannerwhile sandwiching liquid crystal therebetween, a plurality of gatesignal lines which are arranged in parallel and a plurality of drainsignal lines which cross the gate signal lines and are arranged inparallel are formed;

regions which are surrounded by the respective signal lines constitutepixel regions, and a thin film transistor which is operated in responseto scanning signals from the gate signal lines, pixel electrodes towhich video signals are supplied from the drain signal lines through thethin film transistor, and counter electrodes to which signals whichconstitute a reference with respect to the video signals are suppliedthrough counter voltage signal lines,are formed on each pixel region;and

the counter voltage signal lines include the counter voltage signallines which extend in the running direction of the gate signal lines byway of an insulation film and are overlapped to the gate signal lines,and the gate signal lines are constituted such that a taper which isflared toward a ground layer side of the gate signal line is formed onat least a side wall face of one of respective sides in the runningdirection of each gate signal line.

(9)

A liquid crystal display with a pair of substrates with liquid crystallayer therebetween, a plurality of gate signal lines and a plurality ofdrain signal lines formed on one of the pair of substrates; at least apixel electrode and a plurality of counter electrodes formed on the oneof the pair of substrates in each pixels, wherein at least one of theplurality of counter electrodes extend along a drain signal lineoverlapping to the drain signal lines with at least one of an insulationfilm therebetween, and the drain signal line has two or more regionswhich differ in distance between a surface of the drain signal line andthe counter electrode.

(10)

A liquid crystal display device with a pair of substrates with liquidcrystal layer therebetween, a plurality of gate signal lines and aplurality of drain signal lines formed on one of the pair of substrates,at least a pixel electrode and a plurality of counter electrodes formedon the one of the pair of substrates in each pixels, wherein at leastone of the plurality of counter electrodes extend along a drain signalline overlapping to the drain signal lines with at least one of aninsulation film therebetween, the drain signal line has at least a taperportion in a cross section view at width direction of the drain signalline.

(11)

A liquid crystal display device according to (10), a width of the drainsignal line is wider at a substrate side of the drain signal line formedthereon than a liquid crystal layer side.

(12)

A liquid crystal display device according to (10), the drain signal linehave a multiplayer structure of a lower layer faced to the substrate andan upper layer,and the width of the lower layer is wider than a width ofthe upper layer.

(13)

A liquid crystal display device with a pair of substrates with liquidcrystal layer therebetween, a plurality of gate signal lines and aplurality of drain signal lines formed on one of the pair of substrates,at least a pixel electrode and a plurality of counter electrodes formedon the one of the pair of substrates in each pixels, wherein the drainsignal line has a three-layered structure in which an intermediate layeris formed of a conductive layer made of Al or an alloy thereof and anuppermost layer and a lowermost layer are formed of conductive layersmade of material other than Al or an alloy thereof, at least one of theplurality of counter electrodes extend along a drain signal lineoverlapping to the drain signal lines with at least one of an insulationfilm therebetween, and width of the lowermost layer is wider than awidth of the uppermost layer, and a width of the intermediate layergradually change its from the width of the lowermost layer to the widthof the uppermost layer.

(14)

A liquid crystal display device according to (13), oxide films formed onthe side wall of the surface of the intermediate layer.

(15)

A liquid crystal display device with a pair of substrates with liquidcrystal layer therebetween, a plurality of gate signal lines and aplurality of drain signal lines formed on one of the pair of substrates,at least a pixel electrode and a plurality of counter electrodes formedon the one of the pair of substrates in each pixels, at least one of theplurality of counter electrodes extend along a gate signal lineoverlapping to the gate signal lines with at least one of an insulationfilm therebetween, the gate signal line has at least a taper portion ina cross section view at width direction of the gate signal line.

(16)

A liquid crystal display device according to (15), a width of the gatesignal line is wider at a substrate side of the gate signal line formedthereon than a liquid crystal layer side.

(17)

A liquid crystal display device according to (15), the gate signal linehave a multiplayer structure of a lower layer faced to the substrate andan upper layer,and the width of the lower layer is wider than a width ofthe upper layer.

(18)

A liquid crystal display device with a pair of substrates with liquidcrystal layer therebetween, a plurality of gate signal lines and aplurality of drain signal lines formed on one of the pair of substrates,at least a pixel electrode and a plurality of counter electrodes formedon the one of the pair of substrates in each pixels, the gate signalline has a three-layered structure in which an intermediate layer isformed of a conductive layer made of Al or an alloy thereof and anuppermost layer and a lowermost layer are formed of conductive layersmade of material other than Al or an alloy thereof, at least one of theplurality of counter electrodes extend along a gate signal lineoverlapping to the gate signal lines with at least one of an insulationfilm therebetween, and width of the lowermost layer is wider than awidth of the uppermost layer, and a width of the intermediate layergradually change its from the width of the lowermost layer to the widthof the uppermost layer.

(19)

A liquid crystal display device according to (18), oxide films formed onthe side wall of the surface of the intermediate layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one embodiment of a pixel of aliquid crystal display device according to the present invention.

FIG. 2 is an equivalent circuit diagram showing one embodiment of theliquid crystal display device according to the present invention.

FIG. 3 is a plan view showing one embodiment of a pixel of a liquidcrystal display device according to the present invention.

FIG. 4 is a cross-sectional view taken along a line IV—IV in FIG. 3.

FIG. 5 is a cross-sectional-view showing one embodiment of an essentialpart of a pixel of the liquid crystal display device according to thepresent invention.

FIG. 6 is a cross-sectional view showing another embodiment of a drainsignal line of the liquid crystal display device according to thepresent invention.

FIG. 7 is a cross-sectional view showing one embodiment of an essentialpart of a pixel of the liquid crystal display device according to thepresent invention.

FIG. 8 is a flowchart showing one embodiment of a manufacturing methodof a liquid crystal display device according to the present invention.

FIG. 9 is a cross-sectional view showing one embodiment of an essentialpart of a pixel of the liquid crystal display device according to thepresent invention.

FIG. 10 is a cross-sectional view showing another embodiment of thepixel of the liquid crystal display device according to the presentinvention.

FIG. 11 is a cross-sectional view showing another embodiment of thedrain signal line of the liquid crystal display device according to thepresent invention.

FIG. 12 is a cross-sectional view showing another embodiment of thepixel of the liquid crystal display device according to the presentinvention.

FIG. 13 is a cross-sectional view showing another embodiment of thepixel of the liquid crystal display device according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a liquid crystal display device according tothe present invention is explained hereinafter in conjunction withdrawings.

Embodiment 1

<<Equivalent Circuit>>

FIG. 2 is an equivalent circuit diagram showing one embodiment of aliquid crystal display device according to the present invention.Although FIG. 2 is the circuit diagram, the drawing is depicted inaccordance with an actual geometric arrangement.

In the drawing, a pair of transparent substrates SUB1, SUB2 which arearranged to face each other in an opposed manner while sandwichingliquid crystal therebetween are provided, wherein the liquid crystal issealed by a sealing material SL which also has a function of fixing theother transparent substrate SUB2 to one transparent substrate SUB1.

On a liquid-crystal-side surface of one transparent substrate SUB1 whichis surrounded by the sealing material SL, gate signal lines GL whichextend in the x direction and are arranged in parallel in the ydirection and drain signal lines DL which extend in the y direction andare arranged in parallel in the x direction are formed.

A region which is surrounded by respective gate signal lines GL andrespective drain signal lines DL constitutes a pixel region and a massof these pixel regions in a matrix array constitute a liquid crystaldisplay part AR.

Further, common counter voltage signal lines CL which run in respectivepixel regions are formed in respective pixel regions which a rearrangedin parallel in the x direction. These counter voltage signal lines CLconstitute signal lines which supply a voltage which is used asreference with respect to a video signal to counter electrodes CT inrespective pixel regions which will be explained later.

On each pixel region, a thin film transistor TFT which is operated inresponse to a scanning signal from the one-side gate signal line GL anda pixel electrode PX to which a video signal is supplied from theone-side drain signal line DL through the thin film transistor TFT areformed.

The pixel electrode PX generates an electric field between the pixelelectrode PX and the counter electrode CT which is connected to thecounter voltage signal line CL and the optical transmissivity of theliquid crystal is controlled in response to this electric field.

Respective one ends of the gate signal lines GL extend over the sealingmaterial SL and the extending ends constitute terminals to which outputterminals of a vertical scanning driving circuit V are connected.Further, to input terminals of the vertical scanning driving circuit V,signals from a printed circuit board which is arranged outside theliquid crystal display panel are inputted.

The vertical scanning driving circuit V is constituted of a plurality ofsemiconductor devices. A plurality of gate signal lines GL which arearranged close to each other are formed into a group. One semiconductordevice is allocated to each group.

In the same manner, respective one ends of the drain signal lines DLextend over the sealing material SL and the extending ends constituteterminals to which output terminals of the video signal driving circuitHe are connected. Further, input terminals of the video signal drivingcircuit He are configured to receive inputting of signals from a printedcircuit board which is arranged outside the liquid crystal displaypanel.

This video signal driving circuit He is also constituted of a pluralityof semiconductor devices. A plurality of drain signal lines DL which arearranged close to each other are formed into a group. One semiconductordevice is allocated to each group.

Further, the counter voltage signal lines CL are connected in common ata right-side end portion in the drawing, for example. A connection lineextends over the sealing material SL and the extending end constitutes aterminal CLT. A voltage which constitutes the reference with respect tovideo signals is supplied from the terminal CLT.

The respective gate signal lines GL are sequentially selected one by onein response to the scanning signals from the vertical scanning circuitV.

Further, to respective drain signal lines DL, the video signal aresupplied at the timing of selection of the gate signal lines GL from thevideo signal driving circuit He.

In the above-mentioned embodiment, the vertical scanning driving circuitV and the video signal driving circuit He are constituted of thesemiconductor devices which are mounted on the transparent substrateSUB1. However, these driving circuits V and He may be constituted ofso-called tape carrier type semiconductor devices which are connectedastride between the transparent substrate SUB1 and the printed circuitboard, for example. Further, when a semiconductor layer of the thin filmtransistor TFT is constituted of poly-crystalline silicon p-Si,semiconductor divices made of the poly-crystalline silicon may be formedon the transparent substrate SUB1 surface together with wiring layers.

<<Constitution of Pixel>>

FIG. 3 is a plan view showing one embodiment of the constitution of thepixel region. Further, FIG. 1 is a cross-sectional view taken along aline I—I in FIG. 3 and FIG. 4 is a cross-sectional view taken along aline IV—IV in FIG. 3.

In respective drawings, on a liquid-crystal-side surface of thetransparent substrate SUB1, first of all, a pair of gate signal lines GLwhich extend in the x direction and are arranged in the y direction inparallel are formed.

These gate signal lines GL surround a rectangular region together with apair of drain signal lines DL which are explained later and this regionconstitutes the pixel region.

Further, simultaneously with the formation of the gate signal lines GL,the counter voltage signal line CL which runs parallel to the gatesignal lines GL at the center of each pixel region, for example, isformed.

On the surface of the transparent substrate SUB1 on which the gatesignal lines GL and the counter voltage signal lines CL are formed inthis manner, an insulation film GI made of SiN, for example, (see FIG.1, FIG. 4) is formed such that the insulation film GI also covers thegate signal lines GL and the counter voltage signal lines CL.

The insulation film GI has a function of an interlayer insulation filmfor the gate signal lines GL in the regions where the drain signal linesDL which are explained later are formed, has a function of a gateinsulation film in the regions where the thin film transistors TFT whichwill be explained later are formed, and has a function of one ofdielectric films in regions where capacitive elements Cstg which will beexplained later are formed.

Further, on a surface of the insulation film GI, semiconductor layers ASwhich are made of amorphous Si, for example, are formed such that thesemiconductor layers AS are overlapped to portions of the gate signallines GL.

Each semiconductor layer AS constitutes a semiconductor layer of thethin film transistor TFT. By forming a drain electrode SD1 and a sourceelectrode SD2 on an upper surface of the semiconductor layer AS, it ispossible to constitute a MIS type transistor having an inverse staggerstructure which uses a portion of the gate signal line as a gateelectrode.

Here, the drain electrode SD1 and the source electrode SD2 are formedsimultaneously with the formation of the drain signal line DL.

That is, the drain signal lines DL which extend in the y direction andare arranged in parallel in the x direction are formed, then, portionsof the drain signal lines DL are extended over the upper surfaces of thesemiconductor layers AS so as to form the drain electrodes SD1, and thesource electrodes SD2 are formed spaced apart from the drain electrodesSD1 by a length of a channel of the thin film transistor TFT.

Here, with respect to the drain signal line DL, tapers which aregradually widened toward the insulation film GI side of the drain signalline DL are formed on side wall faces of respective sides of the drainsignal line DL in the running direction. The reason that such aconstitution is adopted is explained later.

Further, the source electrode SD2 is integrally formed with the pixelelectrode PX which is formed in the inside of the pixel region.

That is, the pixel electrode PX is constituted of a group consisting ofa plurality (two pieces in the drawing) of electrodes which extend inthe y direction and are arranged in parallel in the x direction in theinside of the pixel region. Among a group of these pixel electrodes PX,one end of one pixel electrode PX also functions as the source electrodeSD2, while the other end portion of the pixel electrode PX iselectrically connected to the corresponding other portion of the otherpixel electrode PX.

Although not shown in the drawing, at interfaces between thesemiconductor layer AS and the drain electrode SD1 as well as the sourceelectrode SD2, thin layers which are doped with impurities of highconcentration are formed and these layers function as contact layers.

These contact layers may be formed such that, for example, impuritylayers of high concentration are already formed on the surface of thesemiconductor layer SD at the time of forming the semiconductor layerSD, and using patterns of the drain electrode SD1 and the sourceelectrode SD2 formed on an upper surface of the semiconductor layer SDas masks, the impurity layers which are exposed from the patterns areetched.

On the surface of the transparent substrate SUB1 on which the thin filmtransistors TFT, the drain signal lines DL, the drain electrodes SD1,the source electrodes SD2 and the pixel electrodes PX are formed, aprotective film PSV (see FIG. 1 and FIG. 4) is formed. This protectivefilm PSV is a film which is provided for obviating the direct contactbetween the thin film transistors TFT and the liquid crystal so as toprevent the deterioration of characteristics of the thin filmtransistors TFT.

Here, the protective film PSV is constituted of a sequentially laminatedbody consisting of a protective film PSV1 which is made of an inorganicmaterial layer such as SiN and a protective film PSV2 which is formed ofan organic material layer made of resin or the like. The reason that theprotective film PSV2 which is made of the organic material layer is usedas the protective film PSV in this manner is that the protective filmPSV2 can reduce the dielectric constant of the protective film PSV perse.

Accordingly, it is needless to say that the protective film PSV may bewholly constituted of the organic material layer without using theinorganic material layer in part.

The counter electrodes CT are formed on an upper surface of theprotective film PSV. Each counter electrode CT is constituted of a groupconsisting of a plurality of electrodes (three electrodes in thedrawing) which extend in they direction and are arranged in parallel inthe x direction in the same manner as the above-mentioned pixelelectrode PX. Further, these respective electrodes are positionedbetween the pixel electrodes PX when viewed as a plan.

That is, the counter electrodes CT and the pixel electrodes PX arerespectively arranged equidistantly in the order of the counterelectrode CT, the pixel electrode PX, the counter electrode CT, thepixel electrode PX, . . . , counter electrode CT from the drain signalline DL at one side to the drain signal line DL at the other side.

Here, the counter electrodes CT which are positioned at both sides ofthe pixel region have portions thereof formed such that the portions areoverlapped to the drain signal lines DL and, at the same time, thecounter electrodes CT are formed in common with the correspondingcounter electrodes CT in the neighboring pixel regions.

In other words, the counter electrodes CT are overlapped to the drainsignal lines DL such that the central axes of the drain signal lines DLare substantially aligned with the center axes of the counter electrodesCT and a width of the counter electrodes CT is set larger than a widthof the drain signal lines DL. The counter electrode CT disposed at theleft side with respect to the drain signal line DL constitutes one ofrespective counter electrodes CT of the left-side pixel region, whilethe counter electrode CT at the right side constitutes one of respectivecounter electrodes CT of the right-side pixel region.

By forming the counter electrodes CT having a width wider than that ofthe drain signal lines DL over the drain signal lines DL in this manner,it is possible to obtain an advantageous effect that lines of electricforces from the drain signal lines DL terminate at the counterelectrodes CT and the termination of lines of electric forces to thepixel electrodes PX can be prevented. This is because that when thelines of electric forces from the drain signal lines DL terminate at thepixel electrodes PX, this gives rise to noises.

Respective counter electrodes CT each of which is constituted of a groupof electrodes are integrally formed with counter voltage signal lines CLmade of the same material as the counter electrode CT. The countervoltage signal lines CL are formed such that the counter voltage signallines CL sufficiently cover the gate signal lines GL. The referencevoltage is supplied to the counter electrodes CT through these countervoltage signal lines CL.

Here, the counter electrodes CT and the counter voltage signal lines CLmay be formed of a non-light-transmitting material such as a metal layeror a light transmitting material such as ITO (Indium Tin Oxide), ITZO(Indium Tin Zinc Oxide), IZO (Indium Zinc Oxide) or the like, forexample.

The counter voltage signal line CL is formed such that the countervoltage signal line CL sufficiently covers the gate signal line GL. Thecounter voltage signal line CL has a portion which is projected from thegate signal line GL. Below such a projected portion of the countervoltage signal line CL, a connecting portion with each pixel electrodePX is positioned. Due to such a constitution, a capacitive element Cstgwhich uses the insulation film GI and the protective film PSV asdielectric films is formed between the pixel electrode PX and thecounter voltage signal line CL.

The capacitive element Cstg is provided with a function of storing videosignals supplied to the pixel electrode PX for a relatively long periodor the like, for example.

Then, on the upper surface of the transparent substrate SUB1 on whichthe counter electrodes CT are formed, an orientation film ORI1 is formedsuch that the orientation film ORI1 also covers the counter electrodesCT. The orientation film ORI1 is a film which comes into direct contactwith the liquid crystal and determines the initial orientation directionof molecules of the liquid crystal with a rubbing formed on a surfacethereof.

As shown in FIG. 3, respective pixel electrodes PX and counterelectrodes CT are constituted such that they have a plurality of bentportions in the longitudinal direction so as to form a zigzag pattern.That is, the liquid crystal display device adopts a so-calledmulti-domain method.

That is, even when the liquid crystal has the same molecular arrangementstate, the polarization state of the transmitting light is changed inresponse to the incident direction of light incident to the liquidcrystal display panel and hence, the transmissivity of light is changedin response to the incident direction.

When a viewing point is inclined obliquely with respect to the viewingangle direction, such a viewing angle dependency of the liquid crystaldisplay panel induces a luminance inverting phenomenon so that theliquid crystal display device exhibits the display characteristics thatimages are colored in color display.

Accordingly, using an imaginary line which connects the bent points ofrespective electrodes as a boundary and the direction of the electricfield which acts between respective electrodes is made different fromeach other between one region and the other region so that it ispossible to compensate for the coloring of images depending on theviewing angle.

In the liquid crystal display device having such a constitution, eachdrain signal line DL has a trapezoidal cross-section in which taperswhich are gradually widened toward a ground layer side are formed onrespective side wall surfaces which are arranged parallel to thelongitudinal direction.

Further, the drain signal lines DL are sufficiently covered with thecounter electrodes CT which are formed over the drain signal lines DL byway of the protective film PSV.

Based on the above-mentioned constitution, as shown in FIG. 5, assuminga distance from a top portion of the drain signal line DL to the counterelectrode CT as d1, a distance from the side wall faces of the drainsignal line DL to the counter electrode CT becomes d2 and this value islarger than d1.

This implies that under the restriction that a film thickness of theprotective film PSV must be set to a given thickness, under therestriction that a cross-sectional area of the drain signal line DL mustbe set to a given value in view of the necessity for setting an electricresistance value of the whole drain signal line DL, and under therestriction that the width of the drain signal line DL must be set to agiven value to enhance the numerical aperture of the pixel region, thecapacitance between the drain signal line DL and the counter electrodeCT can be reduced.

That is, to reduce the capacitance between the drain signal line DL andthe counter electrode CT, first of all, an idea to increase thethickness of the protective film PSV is considered. However,corresponding to the increase of the thickness of the protective filmPSV, the strength of electric field between the pixel electrode PX andthe counter electrode CT is decreased and hence, the driving voltagemust be increased. Accordingly, the increase of the thickness of theprotective film PSV is restricted. Further, there may be considered anidea in which the width of the drain signal line DL is increasedcorresponding to the decrease of the film thickness of the drain signalline DL so as to reduce the capacitance between the drain signal line DLand the counter electrode CT while ensuring the electric resistancevalue of the drain signal line DL. In this case, however, along with theincrease of the width of the drain signal line DL, it becomes necessaryto increase the width of the counter electrode CT (since the counterelectrode CT has a so-called shielding function) and hence, thenumerical aperture of the pixel region is reduced.

In view of the above, when the cross-sectional area of the drain signalline DL is set with respect to the constitution of the drain signal lineDL, it is effective to reduce the width W₁ of the top surface withrespect to the width W₂ of the bottom surface. This is because that aregion where the distance from the side wall surface of the drain signalline DL to the counter electrode CT is d2 (>d1) becomes larger than aregion where the distance from the top surface of the drain signal lineDL to the counter electrode CT is d1 with respect to area.

Also in this case, it is needless to say that the width W₂ of the bottomsurface of the drain signal line DL is restricted by a given numericalaperture which is to be obtained by the pixel region.

Embodiment 2

In view of the gist of the invention described in the embodiment 1, thecross-sectional shape of the drain signal line DL is not always limitedto the trapezoidal shape. For example, as shown in FIG. 6( a), arecessed portion DEN which is extended along the longitudinal directionof the drain signal line DL may be formed on the top surface of thedrain signal line DL. Further, as shown in FIG. 6( b), the number of therecessed portion DEN is not limited to 1 but can be set to a pluralnumber. Still further, a cross-sectional shape of the recessed portionDEN is not limited and may be a triangular shape as shown in FIG. 6( c).

That is, provided that the surface of the drain signal line DL whichfaces the counter electrode CT has at least two regions where thedistance from the counter electrode CT differs from each other, the sameadvantageous effect can be obtained.

Embodiment 3

FIG. 7 is a constitutional view showing another embodiment of the liquidcrystal display device according to the present invention andcorresponds to FIG. 5.

The constitution which makes this embodiment differ from the embodimentshown in FIG. 5 lies in that the drain signal line DL has a two-layeredstructure, wherein tapers are formed on side wall faces of a metal layerDML which constitutes a lower layer by making use of a metal layer UMLwhich constitutes an upper layer.

Here, as a material of the metal layer which constitutes the upperlayer, Mo, Cr, MoW, MoCr, Ti, CoMo or the like can be selected, forexample. On the other hand, as a material of the metal layer whichconstitutes the lower layer, Al, AlNd, AlSi, AlTa, AlTiTa, Cr or thelike can be selected, for example.

FIG. 8 is a flow chart showing one embodiment of a manufacturing methodof the above-mentioned drain signal line.

First of all, as shown in FIG. 8( a), to form the drain signal line DL,a metal layer DML which constitutes a lower layer and a metal layer UMLwhich constitutes an upper layer are formed sequentially on an uppersurface of a ground layer. In this case, the metal layer UML whichconstitutes the upper layer is made of a material which exhibits afaster etching rate than a material of the metal layer DML whichconstitutes the lower layer.

Then, a photo resist film PRE is formed on a whole region of a surfaceof the metal layer UML which constitutes the upper layer and the photoresist film PRE is made to remain on a region where the drain signalline DL is to be formed using a well-known photolithography technique.

Subsequently, as shown in FIG. 8( b), using the remaining photo resistfilm PRE as a mask, the metal layers UML, DML which constitute the upperlayer and the lower layer are collectively etched.

First of all, the metal layer UML which constitutes the upper layer isselectively etched so as to expose a surface of the metal layer DMLwhich constitutes the lower layer.

Then, as shown in FIG. 8( c), the metal layer DML which constitutes thelower layer is etched. The etching is performed, as shown in FIG. 8( d),until a surface of the ground layer is exposed.

In this case, on side wall faces of the metal layer DML whichconstitutes the lower layer which remains below the photo resist filmPRE, tapers which are flared toward the ground layer side are formed.

Thereafter, as shown in FIG. 8( e), by removing the photo resist filmPRE completely, the formation of the drain signal line DL is completed.

Embodiment 4

FIG. 9. is a constitutional view showing another embodiment of theliquid crystal display device according to the present invention andcorresponds to FIG. 5.

The constitution which makes this embodiment differ from the embodimentshown in FIG. 5 lies in that a drain signal line is constituted of ametal layer having a three-layered structure, wherein a width of a metallayer DML which constitutes a lower most layer is set to W₂, a width ofa metal layer UML which constitutes an uppermost layer is set to W₁(W₂ >W ₁) and a width of a metal layer MML which constitutes anintermediate layer is changed from W2 to W1 in the direction from theside of the metal layer DML which constitutes the lowermost layer to theside of the metal layer UML which constitutes the uppermost layer thusforming tapers.

The metal layer MML which constitutes the intermediate layer isconstituted of Al or an Al alloy, while other metal layers UML, DML areconstituted of metal or an alloy thereof other than Al or the Al alloy.

In this case, it is preferable that other metal layers UML, DML areconstituted of metal or an alloy thereof which can suppress theoxidation of Al or the alloy thereof. This is because that Al or thealloy thereof is liable to be easily oxidized and the connectionresistance at an input terminal portion of the drain signal line isincreased and this may cause the distortion of waveforms of the videosignals.

Embodiment 5

FIG. 10 is a constitutional view showing another embodiment of theliquid crystal display device according to the present invention andcorresponds to a cross-sectional view taken along a line X—X in FIG. 3.

In this embodiment, the drain signal line DL adopts a three-layeredstructure in the same manner as the embodiment 4 and, at the same time,an interlayer INV which is served for connecting the counter voltagesignal line CL and the counter electrode CT is formed simultaneouslywith the formation of the drain signal line DL.

Here, the interlayer INV is constituted of a laminated structureconstituted of metal layers equal to those of the drain signal line DL.In this case, respective metal layers UML, DML which constitute anuppermost layer and a lowermost layer may be respectively selectedaiming at the enhancement of contacts between them and the counterelectrode CT and the counter voltage signal line CL.

For example, respective metal layers DML, UML constituting the uppermostlayer and the lowermost layer are formed of MoZr, wherein it isdesirable that an amount of Zr is smaller than an amount of Mo. To bemore specific, it is preferable that the composition is set to Mo-8 wt %Zr. Further, an intermediate layer is formed of AlNd, wherein it isdesirable that an amount of Nd is smaller than an amount of Al. To bemore specific, it is preferable that the composition is set to Al-9.8 wt% Nd.

Further, it is also possible to obtain the same advantageous effect byusing a so-called rare-earth element in place of Zr or Nd.

Further, it is preferable that the film thicknesses of respective metallayers UML, DML which constitute the uppermost layer and the lowermostlayer are smaller than the thickness of the metal layer MML whichconstitutes the intermediate layer. This is because that such astructure can enhance the reduction of resistance and the capacitancereduction effect due to the shape. In view of the above, it ispreferable that the film thickness of the metal layer MML constitutingthe intermediate layer is set to a value which is equal to or more thanfour times the film thickness of the metal layer UML which constitutesthe uppermost layer.

Embodiment 6

This embodiment shows a modification of the drain signal line DL havingthe three-layered structure shown in FIG. 5. This embodiment is, asshown in FIG. 11, characterized in that oxide films OXL are formed ontapered surfaces. This provision is made for preventing a phenomenonthat when the metal layer MML which constitutes the intermediate layermade of Al or an alloy thereof is exposed, a hillock occurs from themetal layer MML.

Accordingly, it is possible to prevent the occurrence of a phenomenonthat the line resistance which constitutes the intermediate layer isoxidized as time lapses and the line resistance of the drain signallines DL is changed whereby the reliability of the liquid crystaldisplay device is enhanced.

Here, the oxide films OXL can be formed by following methods. First ofall, by bringing the drain signal line DL having a three-layeredstructure which forms tapers on the side wall faces thereof into anoxygen plasma treatment, the oxide films OXL can be formed on thetapered side wall faces. In this case, it is preferable to use non-Albased metal as a material of the metal layer UML which constitutes theuppermost layer. This is because that the non-Al based metal can preventthe increase of connection resistance.

As another method, a so-called anodizing processing is performed. Thatis, after forming the drain signal lines DL each having thethree-layered structure which uses an Al-based metal layer as theintermediate layer and forms tapers at side wall faces thereof on thesubstrate, the substrate is immersed into an electrolytic solution.Here, the drain signal line DL constitutes an anode and a metal platewhich constitutes a cathode is simultaneously immersed into theelectrolytic solution. Then, by supplying electricity to the anode andthe cathode, the anodic oxide films OXL are formed on the tapered sidewall faces. Also in this case, it is preferable that the material of themetal layer UML which constitutes the uppermost layer is formed ofnon-Al based metal.

Further, as still another method, by heating the drain signal line DLhaving the three-layered structure which forms tapers on side wall facesthereof under atmosphere where oxygen is present, thermally oxidizedfilms are formed on the side wall faces. In this case, it is desirablethat heating is performed at a temperature of not more than 100 degreecentigrade.

Due to such heating, it is possible to alleviate stress generated in theinside of the drain signal line DL having a multi-layered structure.This implies that the disconnection due to stress which occurs withrespect to the drain signal line DL after use of the drain signal lineDL for a long period can be decreased.

This method can be used simultaneously with the above-mentioned twoother methods. This is because that by adding the heating step, thestress generated in the inside of the drain signal line DL can bealleviated.

Embodiment 7

This embodiment adopts a structure in which, while the drain signallines DL maintain the rectangular cross section as it is as in the caseof conventional liquid crystal display device as shown in FIG. 12,recessed portions are formed in regions on a surface of the protectivefilm PSV which constitutes the ground layer for the counter electrodesCT above the drain signal lines DL except for regions where the counterelectrodes CT (at least the counter electrodes CT which are overlappedto the drain signal lines) are formed.

Such protective film PSV can be formed without increasing the number ofsteps using a photolithography technique which adopts a so-called halfexposure method.

Also due to such a constitution, the distance between the drain signalline DL and the counter electrode CT can be increased and hence, thecapacitance between the drain signal line DL and the counter electrodeCT can be reduced.

Embodiment 8

This embodiment, as shown in FIG. 13, premises the constitution shown inthe embodiment 7, wherein tapers are formed on side wall faces of thedrain signal line DL. Due to such a constitution, the capacitancegenerated between the drain signal line DL and the counter electrode CTcan be further reduced.

Also in this case, the drain signal line DL may be constituted in amulti-layered structure to obtain the advantageous effects described inthe above-mentioned embodiments.

Embodiment 9

Although the present invention has been explained by focusing on thedrain signal lines DL in the above-mentioned respective embodiments, itis needless to say that the present invention is not limited to thedrain signal lines DL and is applicable to the gate signal lines GL.

This is because that when the counter voltage signal lines CL which areconnected to the counter electrodes CT are present over the gate signallines GL, the capacitance between them becomes undesirable and therearises the same situation as in the case of the drain signal lines DL.

Embodiment 10

In the above-mentioned embodiments, with respect to the drain signallines DL and the gate signal lines GL, the tapers formed on side wallfaces are formed on side wall faces of respective sides extending in therunning direction of the signal lines. However, it is needless to saythat the present inventions are not limited to such taper formation andare applicable to the taper formation in which the taper is formed onone of side wall faces.

As can be clearly understood from the foregoing explanations, accordingto the liquid crystal display devices of the present inventions, thecapacitance of the drain signal lines with respect to the counterelectrodes can be reduced, for example.

1. A device comprising: an upper conductive element, an insulatingelement, a lower conductive element formed on a same substrate, theinsulating element being arranged between the upper conductive elementand the lower conductive element; wherein a number of layers which formthe upper conductive element is smaller than a number of layers whichform the insulating element, the number of layers which form theinsulating element is smaller than a number of layers which form thelower conductive element, the upper conductive element is thinner thanthe lower conductive element, an insulating layer of the insulatingelement arranged at the upper conductive element side is thicker than aninsulating layer of the insulating element arranged at the lowerconductive element side, and the lower conductive element include alayer thicker than the upper conductive element and a layer thinner thanthe upper conductive element.
 2. A device according to claim 1, whereinthe device is a display device.
 3. A device according to claim 2,wherein the device is a liquid crystal display device.
 4. A deviceaccording to claim 3, wherein the lower conductive element is a drainsignal line and the upper conductive element is a counter electrode. 5.A device according to claim 1, wherein the lower conductive element hasa larger taper angle than a taper angle of the upper conductive element.6. A device according to claim 3, wherein the lower conductive elementhas a larger taper angle than a taper angle of the upper conductiveelement.
 7. A device according to claim 1, wherein the upper conductiveelement and the lower conductive element have an overlapping portionwith the insulating element therebetween.
 8. A device according to claim7, wherein the device is a display device.
 9. A device according toclaim 8, wherein the device is a liquid crystal display device.
 10. Adevice according to claim 9, wherein the lower conductive element is adrain signal line and the upper conductive element is a counterelectrode.
 11. A device according to claim 7, wherein the lowerconductive element has a larger taper angle than a taper angle of theupper conductive element.
 12. A device according to claim 8, wherein thelower conductive element has a larger taper angle than a taper angle ofthe upper conductive element.
 13. A device according to claim 1, whereinthe lower conductive element includes one layer thicker than the upperconductive element and two layers thinner than the upper conductiveelement.
 14. A device according to claim 9, wherein the lower conductiveelement includes one layer thicker than the upper conductive element andtwo layers thinner than the upper conductive element.
 15. A deviceaccording to claim 1, wherein the insulating element is wider than theupper conductive element and the upper conductive element is wider thanthe lower conductive element.
 16. A device according to claim 9, whereinthe insulating element is wider than the upper conductive element andthe upper conductive element is wider than the lower conductive element.